vo_opengl: draw subtitles directly onto the video

This has a number of user-visible changes:

1. A new flag blend-subtitles (default on for opengl-hq) to control this
   behavior.

2. The OSD itself will not be color managed or affected by
   gamma controls. To get subtitle CMS/gamma, blend-subtitles must be
   used.

3. When enabled, this will make subtitles be cleanly interpolated by
   :interpolation, and also dithered etc. (just like the normal output).

Signed-off-by: wm4 <wm4@nowhere>

DOCS/man/vo.rst

@@ -652,6 +652,17 @@ Available video output drivers are:
         Default is 128x256x64.
         Sizes must be a power of two, and 512 at most.
 
+    ``blend-subtitles``
+        Blend subtitles directly onto upscaled video frames, before
+        interpolation and/or color management (default: no). Enabling this
+        causes subtitles to be affected by ``icc-profile``, ``target-prim``,
+        ``target-trc``, ``interpolation``, ``gamma`` and ``linear-scaling``.
+        It also increases subtitle performance when using ``interpolation``.
+
+        The downside of enabling this is that it restricts subtitles to the
+        visible portion of the video, so you can't have subtitles exist in the
+        black margins below a video (for example).
+
     ``alpha=<blend|yes|no>``
         Decides what to do if the input has an alpha component (default: blend).
 

sub/osd.c

@@ -332,6 +332,8 @@ void osd_draw(struct osd_state *osd, struct mp_osd_res res,
             continue;
         if ((draw_flags & OSD_DRAW_SUB_ONLY) && !obj->is_sub)
             continue;
+        if ((draw_flags & OSD_DRAW_OSD_ONLY) && obj->is_sub)
+            continue;
 
         if (obj->sub_state.dec_sub)
             sub_lock(obj->sub_state.dec_sub);

sub/osd.h

@@ -180,6 +180,7 @@ void osd_set_nav_highlight(struct osd_state *osd, void *priv);
 enum mp_osd_draw_flags {
     OSD_DRAW_SUB_FILTER = (1 << 0),
     OSD_DRAW_SUB_ONLY   = (1 << 1),
+    OSD_DRAW_OSD_ONLY   = (1 << 2),
 };
 
 void osd_draw(struct osd_state *osd, struct mp_osd_res res,

video/out/gl_osd.c

@@ -401,7 +401,7 @@ struct gl_vao *mpgl_osd_get_vao(struct mpgl_osd *ctx)
 }
 
 void mpgl_osd_generate(struct mpgl_osd *ctx, struct mp_osd_res res, double pts,
-                       int stereo_mode)
+                       int stereo_mode, int draw_flags)
 {
     for (int n = 0; n < MAX_OSD_PARTS; n++)
         ctx->parts[n]->num_subparts = 0;
@@ -413,6 +413,6 @@ void mpgl_osd_generate(struct mpgl_osd *ctx, struct mp_osd_res res, double pts,
     ctx->display_size[0] = s_res.w = s_res.w / div[0];
     ctx->display_size[1] = s_res.h = s_res.h / div[1];
 
-    osd_draw(ctx->osd, s_res, pts, 0, ctx->formats, gen_osd_cb, ctx);
+    osd_draw(ctx->osd, s_res, pts, draw_flags, ctx->formats, gen_osd_cb, ctx);
     ctx->stereo_mode = stereo_mode;
 }

video/out/gl_osd.h

@@ -13,7 +13,7 @@ void mpgl_osd_destroy(struct mpgl_osd *ctx);
 void mpgl_osd_set_options(struct mpgl_osd *ctx, bool pbo);
 
 void mpgl_osd_generate(struct mpgl_osd *ctx, struct mp_osd_res res, double pts,
-                       int stereo_mode);
+                       int stereo_mode, int draw_flags);
 enum sub_bitmap_format mpgl_osd_get_part_format(struct mpgl_osd *ctx, int index);
 struct gl_vao *mpgl_osd_get_vao(struct mpgl_osd *ctx);
 void mpgl_osd_draw_part(struct mpgl_osd *ctx, int vp_w, int vp_h, int index);

video/out/gl_video.c

@@ -183,6 +183,7 @@ struct gl_video {
 
     struct fbotex indirect_fbo;         // RGB target
     struct fbotex chroma_merge_fbo;
+    struct fbotex blend_subs_fbo;
     struct fbosurface surfaces[FBOSURFACES_MAX];
 
     int surface_idx;
@@ -350,6 +351,7 @@ const struct gl_video_opts gl_video_opts_hq_def = {
     .alpha_mode = 2,
     .background = {0, 0, 0, 255},
     .gamma = 1.0f,
+    .blend_subs = 0,
 };
 
 static int validate_scaler_opt(struct mp_log *log, const m_option_t *opt,
@@ -427,6 +429,8 @@ const struct m_sub_options gl_video_conf = {
         OPT_FLAG("rectangle-textures", use_rectangle, 0),
         OPT_COLOR("background", background, 0),
         OPT_FLAG("interpolation", interpolation, 0),
+        OPT_FLAG("blend-subtitles", blend_subs, 0),
+
         OPT_REMOVED("approx-gamma", "this is always enabled now"),
         OPT_REMOVED("cscale-down", "chroma is never downscaled"),
         OPT_REMOVED("scale-sep", "this is set automatically whenever sane"),
@@ -540,6 +544,7 @@ static void uninit_rendering(struct gl_video *p)
 
     fbotex_uninit(&p->indirect_fbo);
     fbotex_uninit(&p->chroma_merge_fbo);
+    fbotex_uninit(&p->blend_subs_fbo);
 
     for (int n = 0; n < FBOSURFACES_MAX; n++)
         fbotex_uninit(&p->surfaces[n].fbotex);
@@ -1337,6 +1342,7 @@ static void pass_convert_yuv(struct gl_video *p)
     cparams.texture_bits = (cparams.input_bits + 7) & ~7;
     mp_csp_set_image_params(&cparams, &p->image_params);
     mp_csp_copy_equalizer_values(&cparams, &p->video_eq);
+    p->user_gamma = 1.0 / (cparams.gamma * p->opts.gamma);
 
     GLSLF("// color conversion\n");
 
@@ -1402,13 +1408,6 @@ static void pass_convert_yuv(struct gl_video *p)
                              lessThanEqual(vec3(0.0181), color.rgb));)
     }
 
-    if (p->user_gamma != 1) {
-        p->use_indirect = true;
-        gl_sc_uniform_f(sc, "user_gamma", p->user_gamma);
-        GLSL(color.rgb = clamp(color.rgb, 0.0, 1.0);)
-        GLSL(color.rgb = pow(color.rgb, vec3(user_gamma));)
-    }
-
     if (!p->has_alpha || p->opts.alpha_mode == 0) { // none
         GLSL(color.a = 1.0;)
     } else if (p->opts.alpha_mode == 2) { // blend
@@ -1548,6 +1547,13 @@ static void pass_colormanage(struct gl_video *p)
     enum mp_csp_prim prim_src = p->image_params.primaries,
                      prim_dst = p->opts.target_prim;
 
+    if (p->user_gamma != 1) {
+        p->use_indirect = true;
+        gl_sc_uniform_f(p->sc, "user_gamma", p->user_gamma);
+        GLSL(color.rgb = clamp(color.rgb, 0.0, 1.0);)
+        GLSL(color.rgb = pow(color.rgb, vec3(user_gamma));)
+    }
+
     if (p->use_lut_3d) {
         // The 3DLUT is hard-coded against BT.2020's gamut during creation, and
         // we never want to adjust its output (so treat it as linear)
@@ -1703,6 +1709,44 @@ static void pass_dither(struct gl_video *p)
           dither_quantization);
 }
 
+// Draws the OSD. If linearize is true, the output will be converted to
+// linear light.
+static void pass_draw_osd(struct gl_video *p, int draw_flags, double pts,
+                          struct mp_osd_res rect, int vp_w, int vp_h, int fbo,
+                          bool linearize)
+{
+    mpgl_osd_generate(p->osd, rect, pts, p->image_params.stereo_out, draw_flags);
+
+    p->gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);
+    for (int n = 0; n < MAX_OSD_PARTS; n++) {
+        enum sub_bitmap_format fmt = mpgl_osd_get_part_format(p->osd, n);
+        if (!fmt)
+            continue;
+        gl_sc_uniform_sampler(p->sc, "osdtex", GL_TEXTURE_2D, 0);
+        switch (fmt) {
+        case SUBBITMAP_RGBA: {
+            GLSLF("// OSD (RGBA)\n");
+            GLSL(vec4 color = texture(osdtex, texcoord).bgra;)
+            break;
+        }
+        case SUBBITMAP_LIBASS: {
+            GLSLF("// OSD (libass)\n");
+            GLSL(vec4 color =
+                vec4(ass_color.rgb, ass_color.a * texture(osdtex, texcoord).r);)
+            break;
+        }
+        default:
+            abort();
+        }
+        if (linearize)
+            pass_linearize(p);
+        gl_sc_set_vao(p->sc, mpgl_osd_get_vao(p->osd));
+        gl_sc_gen_shader_and_reset(p->sc);
+        mpgl_osd_draw_part(p->osd, vp_w, vp_h, n);
+    }
+    gl_sc_set_vao(p->sc, &p->vao);
+}
+
 // The main rendering function, takes care of everything up to and including
 // upscaling
 static void pass_render_frame(struct gl_video *p)
@@ -1711,6 +1755,31 @@ static void pass_render_frame(struct gl_video *p)
     pass_read_video(p);
     pass_convert_yuv(p);
     pass_scale_main(p);
+
+    if (p->osd && p->opts.blend_subs) {
+        // Recreate the real video size from the src/dst rects
+        int vp_w = p->dst_rect.x1 - p->dst_rect.x0,
+            vp_h = p->dst_rect.y1 - p->dst_rect.y0;
+        struct mp_osd_res rect = {
+            .w = vp_w, .h = vp_h,
+            .ml = -p->src_rect.x0, .mr = p->src_rect.x1 - p->image_w,
+            .mt = -p->src_rect.y0, .mb = p->src_rect.y1 - p->image_h,
+            .display_par = 1.0,
+        };
+        // Adjust margins for scale
+        double scale[2];
+        get_scale_factors(p, scale);
+        rect.ml *= scale[0]; rect.mr *= scale[0];
+        rect.mt *= scale[1]; rect.mb *= scale[1];
+        finish_pass_fbo(p, &p->blend_subs_fbo, vp_w, vp_h, 0,
+                        FBOTEX_FUZZY_W | FBOTEX_FUZZY_H);
+        double vpts = p->image.mpi->pts;
+        if (vpts == MP_NOPTS_VALUE)
+            vpts = p->osd_pts;
+        pass_draw_osd(p, OSD_DRAW_SUB_ONLY, vpts, rect, vp_w, vp_h,
+                      p->blend_subs_fbo.fbo, p->use_linear);
+        GLSL(vec4 color = texture(texture0, texcoord0);)
+    }
 }
 
 static void pass_draw_to_screen(struct gl_video *p, int fbo)
@@ -1859,60 +1928,12 @@ static void gl_video_interpolate_frame(struct gl_video *p, int fbo,
     }
 }
 
-static void draw_osd(struct gl_video *p)
-{
-    mpgl_osd_generate(p->osd, p->osd_rect, p->osd_pts, p->image_params.stereo_out);
-
-    for (int n = 0; n < MAX_OSD_PARTS; n++) {
-        enum sub_bitmap_format fmt = mpgl_osd_get_part_format(p->osd, n);
-        if (!fmt)
-            continue;
-        gl_sc_uniform_sampler(p->sc, "osdtex", GL_TEXTURE_2D, 0);
-        switch (fmt) {
-        case SUBBITMAP_RGBA: {
-            GLSLF("// OSD (RGBA)\n");
-            GLSL(vec4 color = texture(osdtex, texcoord).bgra;)
-            break;
-        }
-        case SUBBITMAP_LIBASS: {
-            GLSLF("// OSD (libass)\n");
-            GLSL(vec4 color =
-                vec4(ass_color.rgb, ass_color.a * texture(osdtex, texcoord).r);)
-            break;
-        }
-        default:
-            abort();
-        }
-
-        // Apply OSD color correction
-        if (p->use_linear)
-            pass_linearize(p);
-        if (p->user_gamma != 1) {
-            gl_sc_uniform_f(p->sc, "user_gamma", p->user_gamma);
-            GLSL(color.rgb = clamp(color.rgb, 0.0, 1.0);)
-            GLSL(color.rgb = pow(color.rgb, vec3(user_gamma));)
-        }
-        pass_colormanage(p);
-
-        gl_sc_set_vao(p->sc, mpgl_osd_get_vao(p->osd));
-        gl_sc_gen_shader_and_reset(p->sc);
-        mpgl_osd_draw_part(p->osd, p->vp_w, p->vp_h, n);
-    }
-
-    debug_check_gl(p, "after OSD rendering");
-}
-
 // (fbo==0 makes BindFramebuffer select the screen backbuffer)
 void gl_video_render_frame(struct gl_video *p, int fbo, struct frame_timing *t)
 {
     GL *gl = p->gl;
     struct video_image *vimg = &p->image;
 
-    struct mp_csp_params params;
-    mp_csp_copy_equalizer_values(&params, &p->video_eq);
-
-    p->user_gamma = 1.0 / (p->opts.gamma * params.gamma);
-
     gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);
 
     if (!vimg->mpi || p->dst_rect.x0 > 0 || p->dst_rect.y0 > 0 ||
@@ -1939,8 +1960,11 @@ void gl_video_render_frame(struct gl_video *p, int fbo, struct frame_timing *t)
 
     gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);
 
-    if (p->osd)
+    if (p->osd) {
-        draw_osd(p);
+        pass_draw_osd(p, p->opts.blend_subs ? OSD_DRAW_OSD_ONLY : 0,
+                      p->osd_pts, p->osd_rect, p->vp_w, p->vp_h, fbo, false);
+        debug_check_gl(p, "after OSD rendering");
+    }
 
     gl->UseProgram(0);
     gl->BindFramebuffer(GL_FRAMEBUFFER, 0);
@@ -2144,6 +2168,10 @@ static void check_gl_features(struct gl_video *p)
         p->opts.interpolation = false;
         disabled[n_disabled++] = "interpolation (FBO)";
     }
+    if (p->opts.blend_subs && !test_fbo(p, &have_fbo)) {
+        p->opts.blend_subs = false;
+        disabled[n_disabled++] = "subtitle blending (FBO)";
+    }
     if (gl->es && p->opts.pbo) {
         p->opts.pbo = 0;
         disabled[n_disabled++] = "PBOs (GLES unsupported)";

video/out/gl_video.h

@@ -56,6 +56,7 @@ struct gl_video_opts {
     int use_rectangle;
     struct m_color background;
     int interpolation;
+    int blend_subs;
 };
 
 extern const struct m_sub_options gl_video_conf;